Bitcoin for Beginners:

Nakamoto, Satoshi, 2009. Bitcoin: A Peer-to-Peer Electronic Cash System
Szabo, Nick. Formalizing and Securing Relationships on Public Networks 
Szabo, Nick. The idea of smart contracts
Antonopoulos, Andreas, 2015. Mastering Bitcoin.
The Bitcoin Wiki
A developer-oriented series about Bitcoin

Understanding Blockchain:

What is Blockchain and Why Does it Matter
Is the Blockchain Revolution Real

Internet vs Blockchain - Fat Protocols 
Understanding the Lightning Network - Part 1 
Understanding the Lightning Network - Part 2 
Understanding the Lightning Network - Part 3
The Blockchain Academy Blog
Public & Permissioned Blockchains
Data availability & Erasure coding

Blockchain Podcast:


Bitcoin Advanced: 

Mining Bitcoin with pencil and paper
Bitcoin Transaction Malleability
Bitcoin Transaction Decoder
Scripts Playground
Official Developer Reference (version message)
Excellent Free API both for the bitcoin mainnet and testnet

Ethereum Advanced:

Ethereum Whitepaper
Ethereum: A Next Generation Smart Contract & Decentralized Application - Vitalik Buterin

Ethereum General Concepts
List of (some) Available OP_CODES
Ethereum: A Secure Decentralized Generalized Transaction Ledger  aka "The Yellow Paper"
Dapps for Beginners 
Ethereum Security Tips
Mostly good for more in depth EVM and inline assembly
Upgradeable Contracts
A noob Intro to programming Smart Contracts 


Sidechains: Enabling Blockchain Innovations with Pegged Sidechains (Blockstream team)

Private / Permissioned Blockchains: